Cylindrical air filters are used in conjunction with a wide variety of air breathing machinery, including trucks and cars, gas turbines, bulldozers, heavy cranes and other heavy equipment. Typically, this type of filter employs a perforated metal frame and an enclosed, generally cylindrical pleated paper filter medium having inside and outside filtering surfaces. Depending upon the configuration of the machinery and their air intakes, some use the filters in an interior filtering mode, while the others are utilizing the exterior surfaces of the filters to filter and thereby clean the incoming air. Most automobiles employ relatively inexpensive filters that are simply replaced and then discarded when they become dirty, However trucks and other heavy equipment usually employ air filters that are relatively large and expensive to replace. Accordingly, various techniques have been developed to clean these large filters which can thereby be reused. Most often, they are washed in suitable solvents and cleaning solutions. Such washing tends to weaken the paper filter medium so that it is significantly less effective when the filter is being reused.
U.S. Pat. No. 4,808,234 describes an attempt to overcome the disadvantages of solvent cleaning filters by using a "dry" cleaning system wherein dirt, debris and other contaminants are dislodged from the filter and are then collected by a vacuum or other suction device. In this patent, air is supplied simultaneously to the inside and outside surfaces of the cylindrical surfaces of the filter to dislodge dirt from the outside surface. Suction collects this dislodged dirt. As the air pressure is applied, the filter is rotated horizontally about its longitudinal axis. There is no way that dirt can be collected from the inside surface of the filter. In our present invention at hand, the machine can be switched to either mode of operation, that is, inside surface cleaning or outside surface cleaning, as will be shown below. Furthermore, in U.S. Pat. No. 4,808,234, the operator must manually reach into the cabinet of the apparatus and hold the filter while securing it to a spindle. This is awkward and hazardous. In the invention at hand, there are certain safety precautions built into the machine which will be described below.
In the filter cleaning apparatus disclosed in U.S. Pat. No. 5,143,529, the air filter is mounted upright in a cabinet. High pressure and opposing air nozzles are mounted for vertical movement along the inner and outer surfaces of the filter to dislodge debris therefrom. Similarly, inner and outer vacuum nozzles are mounted adjacent to and movable with the air nozzles for suctioning the dislodged debris. Although this apparatus facilitates handling and mounting of the filter and cleans both inside and outside filters, it also exhibits a number of serious disadvantages, for one thing it cannot properly clean many tapered filters that are now commercially available because the inside nozzle often cannot move freely through the central opening of such filters. Additionally, the upright filter rotates during the cleaning process. As a result, when an inside filter is being cleaned, centrifugal forces cause the dirt and debris to be pushed tightly into the interior pleats of the filtermedium. this makes cleaning of the inside surface more difficult. Cleaning is also complicated because the interior dirt and debris falls from the paper filter and much of it drops into corners of the filter, which are inaccessible to the force of the vacuum.
Therefore, the filter is not completely cleaned.
In neither of the above described devices can the user select either inside or outside cleaning alone. In U.S. Pat. No. '234 only outside cleaning is possible. In U.S. Pat. No. '529 both types of cleaning are performed on every filter, although virtually all air filters require only one type of cleaning (either inside or outside). None of the above described filter cleaning devices use a vibrating device or hammer by which dirt and debris is dislodged during the cleaning process.
Our previous U.S. Pat. No. 5,584,900, which issued on Dec. 17, 1996, includes such a pneumatic hammer. This U.S. Pat. No. '900 is hereby incorporated in this specification by reference. The invention of this application constitutes an improvement over the apparatus of our previous patent.